Impacts of non-native plant and animal invaders on gap regeneration in a protected boreal forest |
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Authors: | Jessica M Humber Luise Hermanutz |
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Institution: | (1) Department of Biology, Memorial University of Newfoundland, St. John’s, NL, A1B 3X9, Canada;(2) Present address: Wildlife Division, Department of Environment & Conservation, Government of Newfoundland and Labrador, 117 Riverside Drive, P.O. Box 2007, Corner Brook, NL, A2H 7S1, Canada |
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Abstract: | In balsam fir (Abies balsamea)-dominated boreal forests of Gros Morne National Park, Newfoundland (Canada), non-native Cirsium arvense (Canada thistle) has invaded forest gaps. Its management is complicated by the lack of viable control techniques and an overarching
issue of gap regeneration failure attributed to browsing by non-native moose (Alces alces). This study identifies the impacts of thistle invasion on balsam fir regeneration and explores protocols to re-establish
fir in gaps invaded by thistle and moose. Fir seeds were planted into ten gaps (five natural; five anthropogenic) and the
emergence, growth, herbivory damage, and survival of fir was determined for 2 years amongst five treatments (n = 50 plots; 32 seeds/plot): (1) thistle monocultures in gaps; (2) where aboveground thistle biomass was removed; (3) where
above- and below-ground thistle biomass was removed; (4) non-invaded areas in gaps; and, (5) adjacent uninvaded forest edges.
In addition, 432 fir seedlings (aged 15 months) were transplanted into four forest gaps within the above treatments and followed
for 1 year. Results indicate that invasion of C. arvense negatively affects fir emergence and early survival, and may further contribute to continued balsam fir regeneration failure
independent of future moose densities. However, older fir seedlings transplanted into thistle monocultures experienced a positive
facilitative effect due to the protection thistle provided against small mammal herbivory. Restoration actions that combine
moose density reductions with the planting of fir seedlings offers the most viable long-term strategy to re-establish the
native forest canopy in thistle-invaded gaps and would likely lead to the eventual decline of shade-intolerant C. arvense. |
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